Regenerator with composite insulating wall

ABSTRACT

The present invention relates to a regenerator comprising a bed of energy storage media placed in a chamber, the chamber comprising a shell and an insulating layer placed between said shell and said energy storage media, the insulating layer comprising a structure defining a plurality of cavities, each cavity having a volume greater than 5 cm 3 , at least a portion of said cavities being filled, at least partly, with an insulating material, the minimum thickness of the structural material separating the cavities and the internal volume of the chamber wherein the energy storage media are placed being higher than 2 mm.

TECHNICAL FIELD

The invention relates to a thermal storage regenerator, and to a thermalinstallation comprising such a regenerator.

TECHNOLOGICAL BACKGROUND

The storage of energy, for example heat energy, serves to create a timeoffset between the production and the consumption of said energy.

Heat energy storage is also useful for utilizing soft energies, such assolar energy, which are renewable but are produced intermittently.Energy storage can also be useful for exploiting differences inelectricity prices between “off-peak” hours, during which theelectricity tariffs are the lowest, and “peak” hours, during which thetariffs are the highest. For example, in the case of compressed airenergy storage, generating heat energy which is stored in a thermalregenerator, the compression phases consuming electricity areadvantageously carried out at minimum cost during off-peak hours, whilethe expansion phases producing electricity are carried out during peakhours, in order to supply electricity which can be injected into thegrid, in accordance with demand, at an advantageous tariff.

The heat energy is conventionally stored in a packed bed of energystorage media, for example a pebble bed, placed in a chamber of aregenerator. This chamber may comprise a shell that is internallyinsulated by an insulating layer in order to improve the energyefficiency.

The storage operation, by heat exchange between a stream of heattransfer fluid and the regenerator, is conventionally called the “chargephase”, the heat transfer fluid entering the regenerator during thecharge being called the “charge heat transfer fluid”.

Conventionally, the charge heat transfer fluid enters the regenerator ata temperature, preferably substantially constant, higher than 350° C.,or even higher than 500° C. (and generally lower than 1000° C., or evenlower than 800° C.).

The charge heat transfer fluid then continues its route in theregenerator, while heating the energy storage media with which it is incontact. Its temperature therefore falls progressively to a temperaturetypically between 20° C. and 350° C. The transfer of heat energy cancause an increase in the temperature of the energy storage media(“sensible” heat storage) and/or a phase change of these media (“latent”heat storage).

The heat energy stored can then be restored, by heat exchange between astream of heat transfer fluid and the energy storage media. Thisoperation is conventionally called the “discharge phase”, the heattransfer fluid entering the regenerator during the discharge is called“discharge heat transfer fluid”.

The regenerator thereby undergoes a succession of “cycles”, regular orirregular, each cycle comprising a charge phase, optionally a waitingphase, followed by a discharge phase. The duration of a regular cycle isgenerally longer than 0.5 hour, or even longer than two hours and/orshorter than 48 hours, or even shorter than 24 hours.

“A review on packed bed solar energy storage systems”, Renewable andSustainable Energy Reviews, 14 (2010), p 1059-1069, describes the priorart in the field of regenerators.

A permanent need exists to improve the energy efficiency of theregenerators.

It is an object of the invention to meet this need, at least partially.

SUMMARY OF THE INVENTION

According to the invention, this goal is achieved using a regenerator,in particular a sensible heat regenerator, comprising a bed of energystorage media placed in a chamber, the chamber comprising a shell,preferably metallic, and an insulating layer placed preferably betweensaid shell and said energy storage media or outside said shell.

The insulating layer is characterized in that it comprises a structuredefining a plurality of cavities, each cavity having a volume greaterthan 5 cm³, at least a portion of said cavities being filled, at leastpartly, with an insulating material.

The inventors have discovered that such an insulating layer yields aremarkable energy efficiency. Without being bound by this theory, theyexplain this result by the capacity of the cavities to limit, or evenprevent, gas flows, in the insulating layer. In fact, these flows,resulting from sometimes very high thermal gradients in the insulatinglayer of a regenerator, in particular according to the length of theregenerator, are detrimental to the thermal insulation, and hence to theenergy efficiency.

Preferably, a regenerator according to the invention further comprisesone, and preferably more, of the following optional features:

-   -   The structure is made of a structural material having the        following chemical analysis, in weight percent based on the        oxides and for a total of 100%:        -   25%<Fe₂O₃<90%, preferably Fe₂O₃<70%, and        -   5%<Al₂O₃<30%, and        -   CaO<20%, and        -   TiO₂<25%, and        -   3%<SiO₂<50%, and        -   Na₂O+K₂O<10%, and        -   other oxides<20%    -   The structure is made of a structural material having the        following chemical analysis, in weight percent based on the        oxides and for a total of 100%:        -   40%<Fe₂O₃<60%, and/or        -   Al₂O₃<20%, and/or        -   3%<CaO, and/or        -   5%<TiO₂<15%, and/or        -   5%<SiO₂<20%, and/or        -   Na₂O<5%, and/or        -   other oxides<5%.    -   The structure is made of a structural material of which more        than 50% of the mass consists of one or more of the following        compounds: iron oxides, alumina, magnesia, zirconia, silica,        preferably crystalline silica, titanium dioxide, and calcium        oxide, in particular aluminum-magnesium spinel, steatite,        forsterite and ilmenite (FeTiO₃).    -   The structure is made of a structural material having        -   a chemical composition substantially identical to that of            the material constituting the energy storage media and/or            substantially identical to that of the insulating material,            and/or        -   an open porosity lower than 20%, and/or        -   a compressive strength higher than 10 MPa, and/or        -   a pyroscopic resistance higher than 700° C.    -   The structure consists of a bonding of structural blocks.    -   The thickness of the insulating layer is formed by a plurality        of structural blocks.    -   The minimum thickness of the insulating layer is higher than 150        mm, preferably higher than 400 mm.    -   The thermal resistance of the insulating layer is higher than 1        m²·K/W, preferably higher than 1.2 m²·K/W.    -   The insulating material has a chemical composition such that        Fe₂O₃+Al₂O₃+SiO₂+ZrO₂+B₂O₃+Na₂O+CaO+MgO+K₂O>60%, preferably such        that Fe₂O₃+Al₂O₃+SiO₂+ZrO₂+B₂O₃+Na₂O+CaO+MgO+K₂O>90%.    -   The compound of the insulating material having the highest        weight content is selected from the group consisting of        corundum, spinel MgAl₂O₄, calcined clays, mullite, hibonite,        aluminum titanate, bauxite and combinations thereof.    -   The insulating material has the physical structure of a foam or        of a mixture of fibers.    -   More than 50% by number of the cavities containing insulating        material are through cavities.    -   The cavities account for more than 50% of the volume defined by        the structure.    -   More than 50% by number of the cavities are filled at least        partially, preferably completely, with insulating material.    -   The ratio of the volume of the insulating material of a cavity        to the volume of said cavity is higher than 50%, preferably        substantially equal to 100%.    -   The structural material and the insulating material are        chemically substantially identical.    -   The structural material is chemically substantially identical to        the insulating material and to the material constituting the        energy storage media.    -   The regenerator comprises at least first and second cavities        filled with first and second insulating materials, respectively,        -   the first and second cavities having different shapes and/or            volumes and/or bulk densities and/or orientations and/or            filling ratios with the first and second insulating            materials and/or        -   the first and second insulating materials having different            chemical compositions and/or physical structures and/or            densities.    -   The cavities are arranged so that any imaginary straight line        crossing the insulating layer in the direction of the thickness        of said insulating layer necessarily passes through at least one        cavity.    -   The weight of the bed is higher than 700 tonnes.

The invention also relates to a thermal installation comprising:

-   -   a unit producing heat energy, for example a furnace, a solar        tower, a compressor, and    -   a regenerator according to the invention, and    -   a circulating device which, during a charge phase, circulates a        charge heat transfer fluid from the unit producing heat energy        to the regenerator, and then through said regenerator.

In an embodiment, heat transfer fluid from said unit producing heatenergy condenses in said regenerator in the form of an acidic liquidand/or enters the regenerator at a temperature lower than 1000° C. andhigher than 350° C., or even lower than 800° C. and higher than 500° C.

The unit producing heat energy may comprise a compressor.

In an embodiment, the thermal installation further comprises a heatenergy consumption unit, the circulating device circulating, during adischarge phase, a discharge heat transfer fluid through saidregenerator, and then from said regenerator to the heat energyconsumption unit. The heat energy consumption unit may comprise aturbine.

BRIEF DESCRIPTION OF THE FIGURES

Other objects, aspects, properties and advantages of the presentinvention will further appear in light of the description and theexamples that follow and the examination of the appended drawing inwhich:

FIGS. 1 a and 1 b schematically show a thermal installation according tothe invention during a charge phase and a discharge phase, respectively;

FIG. 2 schematically shows the regenerator of the thermal installationin FIG. 1;

FIGS. 3 a and 3 b show a plan and perspective view of two examples ofbrick suitable for the fabrication of a regenerator according to theinvention.

In FIGS. 3 a and 3 b, identical references are used to denote identicalor similar members. In FIG. 3 b, the references have however been givena “prime” sign.

DEFINITIONS

A “cavity” is a volume bounded by a wall. A cavity may be open orclosed.

Unless otherwise indicated, a “filling” of a cavity with insulatingmaterial does not mean that the cavity is completely filled withinsulating material.

“Unit producing heat energy” means not only units which are specificallyintended to generate heat energy, like a solar tower, but also unitswhich generate heat energy when operated, for example a compressor.

The term “thermal installation” should also be understood in the broadsense, as meaning any installation comprising a unit producing heatenergy.

The term “heat energy consumption unit” designates an element capable ofreceiving heat energy. It may in particular cause an increase in thetemperature of the consumption unit (for example in the case of heatinga building) and/or a conversion to mechanical energy (for example in agas turbine).

In the present description, for the sake of clarity, the terms “chargeheat transfer fluid” and “discharge heat transfer fluid” mean the heattransfer fluid flowing in the regenerator during a charge phase andduring a discharge phase, respectively.

“Bed” of energy storage media means a set of such media at least partlysuperimposed upon one another.

“Preform” conventionally means a set of particles joined by a binder,generally temporary, and whose microstructure evolves during sintering.

“Sintering” means a heat treatment whereby particles of a preform areprocessed to form a matrix binding other particles of said preformtogether.

For the sake of clarity, the term “red mud” means the liquid or pastyby-product issuing from a method for producing alumina and thecorresponding dried product.

The oxide contents are related to the total contents for each of thecorresponding chemical elements, expressed in the most stable oxideform, according to the usual convention in the industry.

Unless otherwise indicated, all the percentages are weight percentages,based on the oxides.

“Containing a” or “comprising a” means “comprising at least one” unlessotherwise indicated.

DETAILED DESCRIPTION Thermal Installation

A thermal installation 2 according to the invention, as shown in FIGS. 1a and 1 b, comprises a unit producing heat energy 4, optionally a heatenergy consumption unit 6, a circulating device 7, optionally a cavitynot shown, and a regenerator 10.

The unit producing heat energy 4 may be intended for producing heatenergy, for example a furnace or a solar tower.

Said circulating device circulates, during a charge phase, a charge heattransfer fluid from the unit producing heat energy to the regenerator,and then through said regenerator.

In an embodiment, the unit producing heat energy comprises, or evenconsists of, a compressor, for example supplied mechanically orelectrically by an incineration plant or an electricity generatingplant, in particular a thermal power, solar energy, wind energy,hydropower, or tidal power plant.

The compression of a gaseous fluid, preferably adiabatic, leads to thestorage of energy therein by increasing its pressure and itstemperature.

The energy resulting from the increase in pressure can be stored bystoring the pressurized fluid. The restoration of this energy may resultfrom an expansion, for example in a turbine.

The energy resulting from the increase in temperature can be stored in aregenerator according to the invention. The restoration of this energythen results from a heat exchange with the regenerator.

The heat energy may be a production by-product, that is to say, may notbe desired as such.

Preferably, the unit producing heat energy produces more than 50 kW, oreven more than 100 kW of heat energy, or even more than 300 kW, or evenmore than 1 MW, or even more than 5 MW. The invention is in factparticularly intended for high-capacity industrial installations.

The unit producing heat energy may comprise a heat exchanger adapted fordirect or indirect heat exchange with the regenerator.

Preferably, a thermal installation according to the invention comprisesa heat energy consumption unit 6, said circulating device circulating,during a discharge phase, a discharge heat transfer fluid through saidregenerator, then from said regenerator to the heat energy consumptionunit.

The heat energy consumption unit 6 may be in particular a building or aset of buildings, a reservoir, a basin, a turbine coupled with agenerator for generating electricity, an industrial installationconsuming steam, such as, for example, a paper pulp manufacturinginstallation.

In the embodiment shown, the heat energy consumption unit 6 comprises aheat exchanger 6 a adapted for heat exchange between discharge heattransfer fluid issuing from the regenerator 10 (FIG. 1 b) and asecondary circuit 6 b in which a secondary heat transfer fluid flows.The secondary circuit is configured for implementing a heat exchangebetween the heat exchanger 6 a and, for example, a building 6 c.

The circulating device 7 comprises a charge circuit 7 a and a dischargecircuit 7 b through which a charge heat transfer fluid and a dischargeheat transfer fluid may flow, respectively. These charge and dischargecircuits serve to implement a heat exchange between the unit producingheat energy 4 and the regenerator 10 during the charge phase, and theregenerator 10 and the heat energy consumption unit 6 during thedischarge phase, respectively.

The circulating device 7 conventionally comprises a set of lines, valvesand pumps/blowers/extractors controlled in order to make the regenerator10 communicate selectively

-   -   with the unit producing heat energy so that it can receive the        charge heat transfer fluid leaving said unit, during a charge        phase (circuit 7 a), and    -   with the heat energy consumption unit so that the heated        discharge heat transfer fluid leaving the regenerator can        transfer heat energy to said consumption unit, during a        discharge phase (circuit 7 b),        and in order to force the flow of the charge heat transfer fluid        (arrows in FIG. 1 a) and/or the discharge heat transfer fluid        (arrows in FIG. 1 b) through the regenerator.

The temperature of the charge heat transfer fluid entering theregenerator during a charge phase is preferably lower than 1000° C., oreven lower than 800° C., and/or preferably higher than 350° C., or evenhigher than 500° C.

The charge and discharge heat transfer fluids may or may not be of thesame type.

The charge heat transfer fluid and/or the discharge heat transfer fluidmay be a gas, for example air, water vapor, or a heat transfer gas, ormay be a liquid, for example water or a thermal oil.

In an embodiment, the energy storage media are in permanent or temporarycontact with an acidic liquid having a pH lower than 6, or even lowerthan 5.5, or even lower than 5, or even lower than 4.5, or even lowerthan 4, in particular that is aqueous. The invention is in factparticularly advantageous under these conditions.

However, the invention is not limited to particular heat transferfluids.

Preferably, in particular when the charge and discharge heat transferfluids are of the same type and when the charge heat transfer fluid hasundergone an increase in pressure, for example to 50 bar, or even 100bar, or even 150 bar, the thermal installation may comprise a cavity fortemporarily storing the charge heat transfer fluid, issuing cooled fromthe regenerator. The volume of the cavity is typically higher than 20000 m³, or even higher than 100 000 m³.

The cavity preferably has low permeability, or is even impervious to thecharge heat transfer fluid.

The regenerator 10, shown in greater detail in FIG. 2, comprises a bed11 of energy storage media 12 placed in a chamber 14.

Bed of Energy Storage Media

Preferably, the regenerator is a sensible heat regenerator, that is tosay, the material of the energy storage media and the charge anddischarge temperatures are determined so that the energy storage mediaremain solid during the operation of the thermal installation. It is infact in a sensible heat regenerator that the probabilities ofcondensation of the heat transfer fluid are the highest.

Preferably, the material of the energy storage media incorporatesresidues from alumina production, in particular by the Bayer process,said process being described in particular in “Les techniques del′ingénieur”, article “métallurgie extractive de l′aluminium”, referenceM2340, editions T.I., published Jan. 10, 1992 (in particular chapter 6starting on page M2340-13 and FIG. 7 on page M2340-15).

Preferably, the energy storage media are obtained by sintering a preformresulting from the shaping of an initial feed comprising more than 10%,preferably more than 30%, preferably more than 50%, preferably more than60%, preferably more than 70%, preferably more than 80% of red mudissuing from the implementation of a Bayer process, expressed as weightpercent on the basis of dry matter of the initial feed. Said red mudsmay optionally be converted before use, for example during washingand/or drying steps.

Preferably, the energy storage media have the following chemicalanalysis, in weight percent based on the oxides and for a total of 100%:

-   -   25%<Fe₂O₃<90%, or even Fe₂O₃<85%, or even Fe₂O₃<80%, or even        Fe₂O₃<75%, or even Fe₂O₃<70%, or even Fe₂O₃<65%, or even        Fe₂O₃<60% and/or preferably Fe₂O₃>30%, preferably Fe₂O₃>35%,        preferably Fe₂O₃>40%, or even Fe₂O₃>45%, or even Fe₂O₃>50%, and    -   5%<Al₂O₃<30%, preferably Al₂O₃<20%, and    -   CaO<20%, and    -   TiO₂<25%, preferably TiO₂<20%, preferably TiO₂<15%, and    -   3%<SiO₂<50%, or even SiO₂<40%, or even SiO₂<30%, or even        SiO₂<20%, or even SiO₂<15%, and    -   Na₂O+K₂O<10%, or even Na₂O+K₂O<5%, and    -   Fe₂O₃+Al₂O₃+CaO+TiO₂+SiO₂+Na₂O+K₂O>80%, preferably        Fe₂O₃+Al₂O₃+CaO+TiO₂+SiO₂+Na₂O+K₂O>85%, or even        Fe₂O₃+Al₂O₃+CaO+TiO₂+SiO₂+Na₂O+K₂O>90%, or even        Fe₂O₃+Al₂O₃+CaO+TiO₂+SiO₂+Na₂O+K₂O>95% and    -   other oxides: complement to 100%.

Preferably, the energy storage media consist of over 90%, preferablyover 95%, preferably over 99% oxides.

Preferably, the energy storage media are made from a sintered material,preferably sintered at a temperature between 1000° C. and 1500° C.,preferably during a holding time at this temperature longer than 0.5hour and preferably shorter than 12 hours, and preferably in anoxidizing atmosphere, preferably in air.

The shapes and dimensions of the energy storage media 12 are notlimiting. Preferably, however, the smallest dimension of an energystorage medium is higher than 0.5 mm, or even higher than 1 mm, or evenhigher than 5 mm, or even higher than 1 cm and/or preferably lower than50 cm, preferably lower than 25 cm, preferably lower than 20 cm,preferably lower than 15 cm. Preferably, the largest dimension of anenergy storage medium is lower than 10 meters, preferably lower than 5meters, preferably lower than 1 meter.

The energy storage media 12 may in particular have the shape of ballsand/or granules and/or solid bricks and/or openwork bricks, and/orcruciform elements and/or double cruciform elements and/or solidelements and/or openwork elements like those described in U.S. Pat. No.6,889,963 and/or described in U.S. Pat. No. 6,699,562.

The energy storage media are assembled in the chamber 14 in order toconstitute the bed 11.

The bed may be organized, for example by bonding the energy storagemedia, or may be disorganized (“bulk”). For example, the bed may havethe form of a mass of crushed parts (without any particular shape, suchas a mass of pebbles).

The height of the bed is preferably greater than 1 m, preferably greaterthan 5 m, preferably greater than 15 m, preferably greater than 25 m, oreven greater than 35 m, or even greater than 50 m.

The weight of the bed is preferably higher than 700 T, preferably higherthan 2000 T, preferably higher than 4000 T, preferably higher than 5000T, and preferably higher than 7000 T.

Chamber

The chamber 14 is provided with a top opening 16 and a bottom opening18.

In an embodiment, the opening of the regenerator through which chargeheat transfer fluid enters the regenerator during a charge phase is theone through which heated discharge heat transfer fluid leaves theregenerator during a discharge phase. Conversely, the opening of theregenerator through which discharge heat transfer fluid to be heatedenters the regenerator during a discharge phase is the one through whichcooled charge heat transfer fluid leaves the regenerator during a chargephase.

Preferably, the opening of the regenerator through which the dischargeheat transfer fluid to be heated enters the regenerator is the bottomopening 18 of the regenerator.

Preferably, the opening of the regenerator through which the heateddischarge heat transfer fluid leaves the regenerator is the top opening16 of the regenerator.

The chamber 14 conventionally comprises a shell 20, conventionallymetallic, for example made of stainless steel, or a carbon steel. Theshell may also consist of the wall of a natural or artificiallyexcavated cavity, optionally provided with an inner lining forstrengthening said wall and/or for leveling the surface in contact withthe energy storage media. The wall of the natural cavity may inparticular be rock.

A cooling system, not shown, may be provided outside the shell,particularly if the regenerator is buried. This system may for examplecirculate air or a liquid, in particular water.

The shell 20 is insulated internally by an insulating layer 24 accordingto the invention, in contact with the energy storage media.

The wall of the shell consists of an upper wall 30, a lower wall 32 anda side wall 34.

Preferably, the insulating layer extends over more than 70%, preferablymore than 80%, preferably more than 90%, preferably more than 95%,preferably over substantially 100%, of the area of the side wall of theshell, or even the total area of the shell.

The minimum thickness, or even the average thickness, of the insulatinglayer (measured from the interior of the regenerator to the exterior ofthe regenerator) is preferably higher than 100 mm, preferably higherthan 150 mm, preferably higher than 200 mm, preferably higher than 300mm, preferably higher than 400 mm, and/or lower than 700 mm, preferablylower than 600 mm.

Preferably, the insulating layer is adapted so that the heat losses fromthe regenerator, under the operating conditions, at the end of a chargeand discharge cycle, are lower than 5%, that is to say that the energyrestored at the end of the discharge phase is higher than 95% of thetotal energy injected into the regenerator at the end of the chargephase. Preferably, these losses are lower than 3%, preferably lower than1%, preferably, the time between the end of a charge phase and thebeginning of the discharge phase being shorter than 48 hours, preferablyshorter than 24 hours.

The thermal resistance of the insulating layer is preferably higher than1 m²·K/W, preferably higher than 1.2 m²·K/W, or even higher than 1.3m²·K/W.

The insulating layer comprises a structure, made of a “structuralmaterial”, defining a plurality of cavities which are at least partlyfilled with an insulating material.

During the operation of the regenerator, and in particular when a heattransfer fluid is humid air, the condensates of the moisture in the aircorrode the materials of the regenerator. Even more, at high pressures,the water present in the air can condense and mix with the othercondensates or pollutants present. The latter may thus make the wateracidic and hence corrosive.

Besides the stresses imposed by the heat transfer fluids, andparticularly the potentially corrosive environment, the energy storagemedia impose physical stresses on the chamber wall with which they arein contact, and in particular stresses resulting from their thermalexpansion and the penetration force which they generate when placed inbulk in the regenerator.

The structure advantageously forms a protective barrier for theinsulating material. Advantageously, the choice of the insulatingmaterial is therefore no longer imposed by the environment prevailing inthe regenerator.

The configuration of the structure, the type of structural material, thenumber of cavities, the volume of the cavities, the bulk density of thecavities (number of cavities per m³), the orientation of the cavities,the chemical composition of the insulating material, the physicalstructure of the insulating material, the density of the insulatingmaterial and the filling ratio are preferably adapted to the localinsulation stresses in the regenerator. A regenerator according to theinvention can thus advantageously comprise an insulating layer that hasa perfectly adapted thermal profile, which therefore serves to optimizethe cost of the regenerator.

Structure Structural Material

The structural material is preferably a ceramic material.

The structural material preferably consists of oxides for more than 90%,preferably more than 95%, preferably more than 99%, preferablysubstantially 100% of its mass.

Preferably, the oxides of the structural material are polycrystalline.

In an embodiment, the structural material has the following chemicalanalysis, in weight percent based on the oxides and for a total of 100%:

-   -   Fe₂O₃>25%, preferably Fe₂O₃>30%, preferably Fe₂O₃>35%,        preferably Fe₂O₃>40%, or even Fe₂O₃>45%, or even higher than        50%, and/or lower than 85%, or even lower than 80%, or even        lower than 75%, or even lower than 70%, or even Fe₂O₃<65%, or        even Fe₂O₃<60%, and    -   5%<Al₂O₃<30%, preferably Al₂O₃<25%, preferably Al₂O₃<20%, and    -   CaO<20%, and, in particular when said material is fabricated        from an initial batch comprising a red mud, CaO>3%, or even        CaO>5%, or even CaO>10%, and    -   TiO₂<25%, preferably TiO₂<20%, preferably TiO₂<15%, and, in        particular when said material is fabricated from an initial        batch comprising a red mud, TiO₂>5%, or even TiO₂>10%, and    -   SiO₂>3%, preferably SiO₂>5%, or even SiO₂>8%, and SiO₂<50%, or        even SiO₂<40%, or even SiO₂<30%, or even SiO₂<20%, or even        SiO₂<15%, and    -   Na₂O+K₂O<10%, preferably Na₂O+K₂O<5%, and    -   other oxides<20%, preferably other oxides<10%, preferably other        oxides<5%, preferably other oxides<3%.

In an embodiment, said structural material has a CaO content preferablylower than 5%, or even lower than 3%, or even lower than 1%.

In an embodiment, said structural material has a TiO₂ content preferablylower than 5%, or even lower than 3%, or even lower than 1%.

Preferably, Fe₂O₃+Al₂O₃+CaO+TiO₂+SiO₂+Na₂O+K₂O>40%,Fe₂O₃+Al₂O₃+CaO+TiO₂+SiO₂+Na₂O+K₂O>50%,Fe₂O₃+Al₂O₃+CaO+TiO₂+SiO₂+Na₂O+K₂O>60%,Fe₂O₃+Al₂O₃+CaO+TiO₂+SiO₂+Na₂O+K₂O>70%,Fe₂O₃+Al₂O₃+CaO+TiO₂+SiO₂+Na₂O+K₂O>80%, preferablyFe₂O₃+Al₂O₃+CaO+TiO₂+SiO₂+Na₂O+K₂O>85%, or evenFe₂O₃+Al₂O₃+CaO+TiO₂+SiO₂+Na₂O+K₂O>90%.

Preferably, the other oxides comprise for over 90% of their mass, oreven consist of, an oxide selected from boron oxide, copper oxides, ironoxides other than Fe₂O₃, and mixtures thereof.

The structural material may for example be ilmenite, a clay, or abauxite.

In an embodiment, the structural material contains more than 50%,preferably more than 60%, preferably more than 70%, or even more than80%, or even more than 90% by weight of aluminum-magnesium spinel, forexample MgAl₂O₄, and/or steatite, and/or forsterite Mg₂SiO₄, and/orilmenite FeTiO₃, and/or iron oxides. Preferably, the mass complement to100% comprises, for over 90% of its mass, or even consists of, an oxideselected from boron oxide, sodium oxide, copper oxides, iron oxides,silica, alumina, and mixtures thereof, and/or a compound of theseoxides. Preferably, the mass complement to 100% comprises for over 90%of its mass, or even consists of, silica, iron oxides or mixturesthereof, and/or a compound of these oxides.

In an embodiment, the structural material is chemically substantiallyidentical to the material constituting the energy storage media.Advantageously, the thermomechanical stresses during the thermal cyclingare decreased.

The minimum thickness of structural material separating the cavities andthe internal volume of the chamber wherein the energy storage media areplaced is preferably higher than 2 mm, preferably higher than 5 mm. Themaximum thickness of structural material separating the cavities and theinternal volume of the chamber wherein the energy storage media areplaced is preferably lower than 20 mm, preferably lower than 15 mm, oreven lower than 12 mm.

The open porosity of the structural material is preferably lower than20%, preferably lower than 18%, or even lower than 15%, or even lowerthan 10%, or even lower than 6% and/or higher than 0.5%, or even higherthan 1%, or even higher than 5%.

The compressive strength of the structural material is preferably higherthan 10 MPa, preferably higher than 20 MPa, preferably higher than 50MPa.

The pyroscopic resistance of the structural material is preferablyhigher than 700° C., or even higher than 800° C., or even higher than900° C., or even higher than 1000° C.

Cavities

The cavities serve to increase the number of possible forms of theinsulating material. For example, the insulating material may be in theform of a powder or a fibrous mat.

The shape and number of cavities are nonlimiting.

The cavities may in particular be tubular, for example polyhedral. Theaxis of a tubular cavity, which defines its length, may be straight orcurved.

The cross-section of a cavity (that is to say perpendicular to its axis)may be circular or not. It may, for example, be parallelepiped-shaped,in particular rectangular parallelepiped-shaped, as shown.

The cross-section of a tubular cavity may be constant along its length,particularly when it has been formed by extrusion, or not.

The cavities may be closed, blind or through cavities, preferablythrough cavities. “Blind” means that a cavity comprises a bottom and aside wall extending from the bottom so as to form a receptacle.Advantageously, the through cavities avoid thermal bridges and improvethe thermal performance of the regenerator.

Preferably, more than 50%, more than 70%, more than 80%, more than 90%,or even 100% by number of the cavities containing insulating materialare through cavities.

The cavities may also have a complex shape. For example, their surfacemay have bulges or roughness, in particular to limit the collapse of theinsulating material.

The largest dimension of any cavity is preferably lower than 50 cm,preferably lower than 40 cm, preferably lower than 30 cm, or even lowerthan 20 cm and preferably higher than 2 cm, or even 4 cm.

The smallest dimension of any cavity is preferably higher than 1 cm,preferably higher than 2 cm and preferably lower than 50 cm, preferablylower than 40 cm, preferably lower than 30 cm, or even lower than 20 cm.

The cavities may or may not all have the same volume. The volume of acavity may in particular be adapted to the insulating material, but alsoto its location in the regenerator.

The volume of any cavity is preferably higher than 10 cm³, preferablyhigher than 25 cm³, preferably higher than 50 cm³ and/or lower than 125000 cm³, preferably lower than 100 000 cm³, preferably lower than 75 000cm³, preferably lower than 50 000 cm³, or even lower than 25 000 cm³, oreven lower than 15 000 cm³, or even lower than 10 000 cm³, or even lowerthan 5000 cm³, or even lower than 2000 cm³. A small cavity volume limitsthe maximum quantity of insulating material that the cavity can contain,and hence the risk of collapse of this insulating material.

It may be preferable to create cavities with small volumes, butcompletely filled, rather than larger, but partially filled cavities.

Preferably, the cavities account for over 50%, over 70%, or even over80% or over 90% of the volume defined by the structure.

The areal density of the cavities is preferably higher than 40% and/orlower than 90%, or even lower than 80%, per square meter of insulatinglayer.

The bulk density of the cavities is preferably higher than 40% and/orlower than 90%, or even lower than 80% per cubic meter of insulatinglayer.

Preferably, over 50%, over 70%, over 80%, over 90%, or even 100% bynumber of the cavities are filled, at least partially, preferablycompletely, with insulating material.

The filling ratio of a cavity containing insulating material (that is tosay the volume of the insulating material divided by the volume of thecavity) may be higher than 50%, higher than 60%, higher than 70%, higherthan 80%, higher than 90%, or even, preferably, substantially 100%.

Preferably, the cavities are dimensioned and/or filled with insulatingmaterial so that the largest dimension of the void volume in any cavityis lower than 50 cm, preferably lower than 40 cm, preferably lower than30 cm, preferably lower than 20 cm, preferably lower than 10 cm.Preferably, the cavities are dimensioned and/or filled with insulatingmaterial so that the length of the void volume in any cavity is lowerthan 50 cm, preferably lower than 40 cm, preferably lower than 30 cm,preferably lower than 20 cm, preferably lower than 10 cm, the lengthbeing measured along the axis of the regenerator corresponding to thegeneral flow direction of the charge and discharge heat transfer fluids.

In a particularly advantageous manner, the circulation of gas within theinsulating layer, in particular due to the high temperature gradients,in particular along the length of the regenerator, is thereby reduced.

The cavities may have any orientation. In an embodiment, all thecavities are parallel to one another, for example in the direction ofthe length of the regenerator.

Preferably, the cavities are arranged so that any imaginary straightline passing through the insulating layer in the direction of thethickness of said insulating layer necessarily passes through at leastone cavity.

The structure may be in a single piece, in particular if the regeneratoris small.

The structure preferably consists of a bonding of shaped parts, or“structural blocks”, the shape of the structural blocks not beinglimiting. Preferably, the structural blocks are jointed, preferably witha jointing material such as a grout, a mortar or a mud, the jointingtechniques being known to a person skilled in the art.

A structural block may comprise a plurality of cavities. It may compriseat least one cavity and at least one, or even a plurality of cavityfractions. A cavity fraction of a structural block participates in thedefinition of a cavity after the bonding of the structural blocks.

The side wall of the regenerator may also comprise expansion joints inthe insulating layer.

Preferably, the Al₂O₃ content of the jointing material is higher than80%, preferably higher than 85%, preferably higher than 90%, or evenhigher than 95%, in weight percent based on the oxides.

In a preferred embodiment, the structural blocks are fabricated andfilled with insulating material before being delivered and assembled toform the insulating layer. The construction of the regenerator isthereby accelerated and is achieved at lower cost.

In an embodiment, the structural blocks are fabricated, delivered andassembled to form the structure before their cavities are filled withinsulating material.

Insulating Material

The insulating material is preferably selected from the group consistingof ceramics, polymers, and mixtures thereof. Preferably, the insulatingmaterial is a ceramic material.

Preferably, the insulating material is composed of oxides for more than90%, preferably for more than 95%, preferably for more than 99%,preferably for substantially 100% of its mass.

Preferably, the insulating material has a chemical composition such thatFe₂O₃+Al₂O₃+SiO₂+ZrO₂+B₂O₃+Na₂O+CaO+MgO+K₂O>60%, preferablyFe₂O₃+Al₂O₃+SiO₂+ZrO₂+B₂O₃+Na₂O+CaO+MgO+K₂O>70%, preferablyFe₂O₃+Al₂O₃+SiO₂+ZrO₂+B₂O₃+Na₂O+CaO+MgO+K₂O>80%, preferablyFe₂O₃+Al₂O₃+SiO₂+ZrO₂+B₂O₃+Na₂O+CaO+MgO+K₂O>90%, in weight percent basedon the oxides.

Even more preferably, the insulating material has a chemical compositionsuch that Fe₂O₃+Al₂O₃+SiO₂+B₂O₃+Na₂O+CaO+K₂O>60%, preferablyFe₂O₃+Al₂O₃+SiO₂+B₂O₃+Na₂O+CaO+K₂O>70%, preferablyFe₂O₃+Al₂O₃+SiO₂+B₂O₃+Na₂O+CaO+K₂O>80%, preferablyFe₂O₃+Al₂O₃+SiO₂+B₂O₃+Na₂O+CaO+K₂O>90%, in weight percent based on theoxides.

Preferably, the complement to 100% is composed of oxides, preferablyselected from BaO, TiO₂, P₂O₅ and mixtures thereof.

The insulating material must be adapted to the maximum temperature atwhich it is used. Thus, glass wool fiber cannot be used if theinsulating material is exposed to a temperature above 400° C., or evenabove 350° C.

The thermal conductivity of the insulating material, in the insulatinglayer, between 20° C. and 800° C., is preferably more than 20%, morethan 50%, more than 100%, more than 200%, more than 300%, more than 400%lower than that of the structural material. Preferably, the thermalconductivity measured at 20° C. is lower than 1 W/m·K, lower than 0.5W/m·K, preferably lower than 0.4 W/m·K, preferably lower than 0.2 W/m·K.

In a particular embodiment, the thermal conductivity of the insulatingmaterial between 20° C. and 800° C. is lower than 0.5 W/m·K, preferablylower than 0.2 W/m·K, and the average thickness of the insulating layeris higher than 300 mm, preferably higher than 400 mm.

The linear thermal expansion coefficient of the insulating material,measured at 500° C., is preferably lower than 15.10⁻⁶° C.⁻¹, preferablylower than 10.10⁻⁶° C.⁻¹, or even lower than 8.10⁻⁶° C.⁻¹.

In an embodiment, the difference between the thermal expansioncoefficients of the insulating and structural materials, at 500° C., isless than 10%, preferably less than 5%, of the thermal expansioncoefficient of the insulating material.

In an embodiment, the thermal expansion coefficients of the insulatingand structural materials at 500° C. are substantially identical. Theinsulation and durability are thereby improved.

In an embodiment, the structural material and the insulating materialare chemically substantially identical. For example, the insulatingmaterial is a foam of the same material as the structural material.

In a preferred embodiment, the structural material is chemicallysubstantially identical to the insulating material and to the materialconstituting the energy storage media.

A person skilled in the art knows how to modify the thermalconductivity, mechanical compressive strength and linear thermalexpansion coefficient of the insulating material.

The insulating material may have any physical structure, for examplerigid, powdery, or fibrous.

The insulating material may, for example, be a molten, poured orsintered product. The insulating material may in particular be a mortar,a concrete, preferably self-placing, or a mud, dry or wet. In anembodiment, the insulating material is a concrete.

The shaping of the insulating material may result from a pouring, inparticular a vibratory pouring, a pressing, in particular a vibratorypressing, a cold pressing, a plastic paste pressing, or an isostaticpressing, a ramming, an extrusion, in particular a co-extrusion servingto produce the structure and to place the insulating material in asingle step of the process, a granulation or a combination of these wellknown techniques. In an embodiment, the shaping of the insulatingmaterial results from a vibratory pouring or a pressing.

In an embodiment, the insulating material is a dry mud installed byramming or by simple pouring.

The cavities make it possible to use an insulating material with anon-rigid structure, for example having the form of a powder or offibers. The insulating material may also, for example, be a foam. Theinsulating material may have an elasticity that promotes its maintenancein the cavity in which it is placed.

Preferably, the insulating material is selected from the group formedby:

-   -   powders, for example a dry mud, preferably comprising alumina        and/or silica and/or aluminosilicates and/or zirconia and/or        iron oxide Fe₂O₃ and/or metal hydroxides, preferably powders        comprising an alumina+silica+zirconia+iron oxide Fe₂O₃ content        higher than 60%, preferably higher than 70%, preferably higher        than 80%, preferably higher than 90%, in weight percent based on        the oxides;    -   mixtures of fibers, such as glass fibers, rock wool fibers,        alumina fibers and mixtures thereof, preferably glass fibers,        rock wool fibers, even more preferably rock wool fibers;    -   foams, in particular:        -   foamed concretes or mortars containing hydraulic binder,            said hydraulic binder being selected from cements,            preferably aluminous cements and/or Portland cements and/or            alumina cements, plaster, geo-polymers and mixtures thereof.            Preferably, said concretes or mortars comprise alumina            and/or silica and/or aluminosilicates and/or zirconia and/or            iron oxide Fe₂O₃ and/or metal hydroxides and/or CaO,            preferably said concretes or mortars comprise an            alumina+silica+zirconia+iron oxide Fe₂O₃+CaO content higher            than 60%, preferably higher than 70%, preferably higher than            80%, preferably higher than 90%, in weight percent based on            the oxides;        -   foams comprising alumina and/or silica and/or            aluminosilicates and/or zirconia and/or iron oxide Fe₂O₃            and/or metal hydroxides, preferably foams comprising an            alumina+silica+zirconia+iron oxide Fe₂O₃ content higher than            60%, preferably higher than 70%, preferably higher than 80%,            preferably higher than 90%, in weight percent based on the            oxides;    -   and mixtures thereof.

Preferably, the insulating material has the physical structure of a foamor of a mixture of fibers.

In an embodiment, the insulating material is rock wool fiber.

In an embodiment, the insulating material is a ceramic foam. All methodsknown to a person skilled in the art to fabricate ceramic foams may beused, in particular those involving the foaming of a slurry, or the useof a pore forming agent or an element capable of forming a gas during aheat treatment or a chemical reaction, thereby generating said foam.

In an embodiment, the insulating material is glass fiber and/or rockwool fiber and the bulk density of the insulating material is between 20and 100 kg/m³.

In an embodiment, the insulating material is a foam, in particular afoamed concrete or a foamed mortar, and the bulk density of theinsulating material is higher than 100 kg/m³, preferably higher than 500kg/m³ and preferably lower than 2000 kg/m³, preferably lower than 1500kg/m³.

The insulating material may or may not adhere to the wall of thecavities. For example, a solid and nonadhesive mass of insulatingmaterial may be introduced into a cavity. It is then preferable for thecavity to have the shape of a receptacle.

Preferably, the cavities are filled with the insulating material bypouring a foamed slurry or a foam precursor slurry, or by stamping, thefoam being previously shaped, cut to the cavity dimensions, and theninserted therein.

Preferably, the insulating material, preferably a ceramic foam, isplaced in the cavities of the structure, in particular of structuralblocks, before the sintering of said structure or of said structuralblocks.

Structural Blocks

The structure may comprise, or even consist of, an assembly ofstructural blocks defining cells, at least a portion of the cells beingfilled, at least partially, with insulating material.

The structural blocks may have any shape. For example, a structuralblock may have the shape of a polyhedron, regular or not, preferablyconvex. The number of sides may in particular be between 3 and 10,preferably between 4 and 8, or even lower than 6. A structural block mayin particular have the shape of a brick, for example with aparallelepiped base, optionally square or rectangular. The structuralblocks may in particular have the shape of hexahedra, keystones, orwedges. They may have a radius of curvature that is preferably higherthan 1 m and preferably lower than 10 m.

The cells of a structural block can be filled in situ, during thefabrication of the insulating layer.

For example, structural blocks having open cells at the upper side, oreven at the underside, may be assembled conventionally, like bricks of awall. The cells of a row of structural blocks are then filled beforetheir upper side is covered with a joint, followed by the next row ofstructural blocks. The cavities of the insulating layer are then definedby the cells of the structural blocks.

Although this embodiment is not preferred, the structural blocks mayalso be assembled so that cells of various structural blockscommunicate. A plurality of cells of blocks thereby define a cavity ofthe insulating layer. This cavity may be filled after assembling thestructural blocks or, preferably, as the structural blocks areassembled, thereby ensuring a uniform filling.

In the preferred embodiment, the cells are filled with insulatingmaterial prior to the fabrication of the insulating layer.

All the cells of a given structural block may have the same shape, orthey may not.

In an embodiment, the partitions separating the cells of a structuralblock have substantially identical average thicknesses. Preferably, thethickness of the partitions separating the cells of a structural blockis substantially constant.

In another embodiment, the partitions separating the cells of astructural block have different thicknesses. For example, radialpartitions, that is to say extending substantially along the directionof the thickness of the insulating layer, may have a lower thicknessthan the thickness of the longitudinal partitions, that is to sayextending substantially perpendicular to the direction of the thicknessof the insulating layer. Advantageously, the thickness of insulatingmaterial along the direction of the thickness of the insulating layermay be maximal, thereby serving to maximize the radial thermalconductivity while preserving a high compressive strength.

The minimum thickness of the partitions, preferably at least the radialpartitions, is preferably higher than 2 mm, or even higher than 5 mm.The maximum thickness of the partitions, preferably at least the radialpartitions, is preferably lower than 20 mm, preferably lower than 15 mm,or even lower than 12 mm, or even lower than 10 mm, or even lower than 8mm.

In an embodiment, the thickness of the insulating layer is formed of nof structural blocks, where n is lower than 10, or even lower than 8, oreven lower than 5.

In an embodiment, the structural blocks have different shapes and/ordimensions according to their position along the thickness of theinsulating layer.

A structural block comprises at least one cell, preferably a pluralityof cells.

Preferably, a structural block comprises a plurality of cells along itsthickness, that is to say, after assembly, from the interior of theregenerator to the exterior of the regenerator. In an embodiment, thecells have different shapes and/or dimensions and/or a different ratioof filling with the insulating material and/or contain differentinsulating materials according to the position of said cells along thethickness of the structural block and/or according to the position ofthe structural block in the regenerator.

For example, the insulating material of the cells close to the interiorof the regenerator may be a ceramic foam or a foamed concrete or afoamed mortar withstanding the high temperatures that prevail inside theregenerator, while the insulating material of the cells close to theexterior of the regenerator may be a polymer foam or a mixture of glassfibers.

In an embodiment, the filling ratio of the cells is a function of thedistance of the cell from the interior of the regenerator. In anembodiment, the cells located nearest to the interior of the regeneratorhave a higher filling ratio than that of the other cells. In anembodiment, the latter are not filled with insulating material.

FIG. 3 a shows a plan view of an example of a hexahedral structuralblock 50 bounded laterally by a wall of a structural block 51 consistingof a portion of internal wall 52, intended to be in contact with theinside volume of the chamber, a portion of external wall 54, intended tobe in contact with the shell of the chamber and opposite the portion ofinternal wall 52, and two portions of side wall 55 and 56, connectingthe portions of internal wall 52 and external wall 54, intended to bejoined, by means of a joint, to adjacent blocks.

The structural block 50 also comprises a radial reinforcing partition57, a longitudinal reinforcing partition 58, and cavity partitions 60,defining, optionally with the radial and longitudinal partitions,internal 62 a and external 62 b cavities. The thickness of the cavitypartitions 60 is lower than that of the wall of a structural block 51and of the radial and longitudinal reinforcing partitions.

The portion of internal wall 52, portion of external wall 54, portionsof side wall 55 and 56, radial reinforcing partition 57, longitudinalreinforcing partition 58, and cavity partitions 60 all extend parallelto the axis Y of the structural block 50, perpendicular to the plane ofthe sheet. The radial reinforcing partition 57 perpendicularlyintersects the longitudinal reinforcing partition 58, along the Y axis.

The internal cavities 62 a, which are tubular with a squarecross-section, are arranged in four rows extending parallel to theportion of internal wall 52, between the portion of internal wall 52 andthe longitudinal reinforcing partition 58. All the internal cavities 62a or only a portion of the internal cavities 62 a, preferably all theinternal cavities 62 a, are partially or completely, preferablycompletely, filled with a first insulating material, not shown.

The external cavities 62 b, which are tubular and have a rectangularcross-section, are arranged in two rows extending parallel to theportion of external wall 54, between the portion of external wall 54 andthe longitudinal reinforcing partition 58. All the external cavities 62b or only a portion of the external cavities 62 b, preferably all theexternal cavities 62 b, are partially or completely, preferablycompletely, filled with a second insulating material, not shown,identical to or different from the first insulating material.

Preferably, the internal cavities 62 a and external cavities 62 b areblind, one of their ends being blocked by a plug, preferably closed,each of their ends being blocked by plugs, not shown.

FIG. 3 b shows another example of a hexahedral structural block 50′which differs in particular from the structural block 50 by the number,shape and arrangement of the cavities 62′. The cavities 62′, having arectangular cross-section, extend parallel to the portions of internalwall 52′ and external wall 54′. They are not aligned in the direction ofthe thickness e of the insulating layer, but offset in pairs, preferablyby a half-length of cavity.

In the prolongation of the cavities 62′, cells 64′, in the shape of acavity fraction, for example in the shape of a half-cavity, are arrangedin the portions of side wall 55′ and 56′. During the assembly of thestructural blocks 50′, the cells 64′ of two adjacent structural blocksmay be arranged facing one another in order to form cavities.

This embodiment serves advantageously to limit the “thermal bridges”between two adjacent structural blocks. In fact, an imaginary line canno longer cross the insulating layer, in the direction of its thickness,without passing through a cavity.

In an embodiment, the cavities formed by placing cells 64′ of twoadjacent structural blocks facing each other are filled with insulatingmaterial after the assembly of these structural blocks.

In an embodiment, the cells 64′ are filled with insulating materialbefore the assembly of the structural blocks. Preferably, the insulatingmaterial then adheres to the surface of the cells 64′.

Examples

The following examples are provided for illustrative purposes and arenonlimiting.

The chemical analyses are carried out by X-ray fluorescence.

The compressive strength is determined according to standard EN993-5.

The pyroscopic resistance is determined according to standard ISO 1893(collapse under load).

The thermal expansion coefficient is determined according to standardEN993-19.

The thermal conductivity of the structural material is determined, atambient temperature, according to the following standard: ASTM E1461-07.

The thermal conductivity of the insulating material is determined, atambient temperature, according to standard NF-EN-12667.

The following assumptions were used to calculate the heat losses:

-   -   cylindrical regenerator, of constant cross-section, diameter 5        m, and in which the bed of energy storage media has a length L,        measured along the X axis of the regenerator, equal to 20 m;    -   charge and discharge heat transfer fluids: dry air;    -   type and volume of energy storage media constant;    -   charge temperature 527° C., or 800 K;    -   total duration of charge phase: 4 hours;    -   discharge temperature 50° C., or 323 K;    -   total duration of discharge phase: 4 hours;    -   outer wall cooling system of the water cooling type: temperature        75° C., heat exchange coefficient 500 W/m²K.

The following formula gives an evaluation of the heat losses across theregenerator walls, after a complete cycle, that is to say, a chargephase and a discharge phase:

J = ∫₀^(t)∫_(S)φ_(T) S. t

In this formula:

-   -   S: outer surface area of the insulating layer in m²;    -   t: duration of a complete cycle;    -   Φ_(t): heat flux on the outer face of the regenerator, in W/m²;    -   J: total losses in the cycle, in J.

Comparative example 1 is a regenerator comprising a shell whereof theentire side wall is insulated by an insulating layer having a constantthickness of 420 mm, consisting of RI30 insulating bricks containing 70%Al₂O₃, sold by Distrisol.

Example 2, according to the invention, is a regenerator comprising ashell whereof the entire side wall is insulated by an insulating layerconsisting of openwork bricks like the one shown in FIG. 3 b, ofdimensions 20 cm×15 cm ans thickness 42 cm, the structural materialbeing a mixture comprising 40% by weight of a clay powder having anAl₂O₃ content of 27%, an SiO₂ content of 65% and 8% of other compounds,and 60% by weight of an iron oxide powder having an Fe₂O₃ content of78.7%, an SiO₂ content of 9%, an Al₂O₃ content of 2.9%, and a MgOcontent of 1.1%. The openwork bricks are shaped by an extrusiontechnique, known to a person skilled in the art, and sintered at atemperature of 1200° C. for 4 hours. The bulk density of the cavities is73% of the volume of the openwork brick. The thickness of the structuralmaterial separating the cavities is 5 mm for the walls oriented in theheat flux direction, and 10 mm for the walls oriented perpendicular tothe heat flux. All the cavities are substantially completely filled bypouring a foamed mortar having the following chemical composition:Al₂O₃: 15%, SiO₂: 35%, Fe₂O₃: 15%, CaO: 30%, other oxides: 5%, saidfoamed mortar being obtained by the following method: Preparation of aslurry containing 40% CEM1 white Portland cement, 30% silica sand havinga median diameter of 150 μm, 30% calcium carbonate having a mediandiameter of 10 μm, water in a water/Portland cement ratio of 0.6 andsatiaxane CX90T xanthan gum sold by Cargill, in a quantity of 0.02% ofthe mass of water. This slurry is mixed, in a beaker having an insidediameter of 130 mm and a height of 180 mm, using a deflocculating bladehaving a diameter of 80 mm, whereof the bottom end is positioned at 10mm from the bottom of the beaker, for 1 minute at a speed of 500 rpm.Sodium lauryl ether sulfate in a quantity of 2% of the quantity of wateris then introduced into the slurry. The volume of slurry being at mostequal to one-third of the volume of the beaker, the mixture is stirredfor 30 seconds at 500 rpm, and then for 1 minute at 1500 rpm. A foamedmortar is obtained and poured into the cavities of the structure. Saidmortar sets at a temperature of 22° C. and 40% relative humidity.

Example 3, according to the invention, is a regenerator comprising ashell whereof the entire side wall is insulated by an insulating layerconsisting of openwork bricks identical to those used in the regeneratorin example 2, all the cavities being substantially completely filled bypouring a ceramic foam obtained by the following method: Preparation ofa slurry containing 40% by weight of a clay powder having an Al₂O₃content of 27%, an SiO₂ content of 65% and 8% of other compounds, and60% by weight of an iron oxide powder having an Fe₂O₃ content of 78.7%,an SiO₂ content of 9%, an Al₂O₃ content of 2.9%, and an MgO content of1.1%, and water in a water/quantity of dry matter ratio of 0.72 andsatiaxane CX90T xanthan gum, sold by Cargill, in a quantity equal to0.6% of the mass of water. This slurry is mixed using a deflocculatingblade having a diameter of 80 mm whereof the bottom end is positioned at10 mm from the bottom of the beaker, in a beaker having an insidediameter of 130 mm and a height of 180 mm, for 1 minute at a speed of500 rpm. W53FL Schäumungsmittel, sold by Zschimmer & Schwarz GmbH, isthen introduced into the slurry in a quantity of 6% of the quantity ofwater. The volume of the slurry being at most equal to one-third of thevolume of the beaker, the mixture is then stirred for 30 seconds at 500rpm, and then for 2 minutes at 1500 rpm. A foam is obtained and ispoured into the cavities of the structure. The combination is thensintered at 1200° C. for 4 hours.

Example 4, according to the invention, is a regenerator comprising ashell whereof the entire side wall is insulated by an insulating layerconsisting of openwork bricks identical to those used in the regeneratorin example 2, all the cavities being substantially completely filledwith unpacked rock wool fibers, having a bulk density of 80 kg/m³ afterthe cavity is filled.

Example 5, according to the invention, is a regenerator comprising ashell whereof the entire side wall is insulated by an insulating layerconsisting of openwork bricks identical to those used in the regeneratorin example 2, all the cavities being substantially completely filled bypouring an alumina foam obtained by the following method: preparation ofa slurry with 24.1% by weight of water and 75.9% by weight of themixture of alumina powders having the following composition, in weightpercent based on said mixture: 39.5% T60/64-65 Mesh tabular alumina, 7%T60/64-325 Mesh tabular alumina, 35% CT3000 SG alumina and 18.5% A10alumina, sold by Almatis, and satiaxane CX90T xanthan gum, sold byCargill, in a quantity equal to 0.5% of the mass of water and glycerinin a quantity equal to 5.5% of the mass of water. This slurry is mixedusing a deflocculating blade having a diameter of 80 mm whereof thebottom end is positioned at 10 mm from the bottom of the beaker, in abeaker having an inside diameter of 130 mm and a height of 180 mm, for60 minutes at a speed of 500 rpm. W53FL Schäumungsmittel, sold byZschimmer & Schwarz GmbH, is then introduced into the slurry in aquantity equal to 10% by weight of the quantity of water. The volume ofthe slurry being at most equal to one-third of the volume of the beaker,the mixture is then stirred for 30 seconds at 500 rpm, and then for 2minutes at 1500 rpm. A foam is obtained. After debinding and sinteringat 1600° C. for 4 hours, the foam blocks are cut to the dimensions ofthe cavities of the structural part and placed therein.

The results obtained are given in table 1 below:

TABLE 1 Example 2 3 4 5 Structural Insulating Structural InsulatingStructural Insulating Structural Insulating 1* material materialmaterial material material material material material Characteristics ofregenerator insulation Type of material RI30 Obtained with FoamedObtained with Clay ceramic Obtained with Rock Obtained with Alumina 40%clay pow- mortar 40% clay pow- foam + iron 40% clay pow- wool 40% claypow- foam der + 60% iron der + 60% iron oxide der + 60% iron der + 60%iron oxide powder oxide powder oxide powder oxide powder Thickness ofinsu- 420 420 420 420 420 lating layer (mm) Open porosity (%) — 70 60 7060 70 — 70 60 Compressive 3 350 — 350 — 350 — 350 — strength (MPa)Pyroscopic resis- 1650 >1000 700 >1000 1200 >1000 — >1000 >1400 tance (°C.) Thermal conduc- 0.45 2.5 0.1 2.5 0.15 2.5 0.05 2.5 0.14 tivity (W/m· K) Equivalent ther- 0.45 0.36 0.42 0.3 0.41 mal conductiv- ity (W/m ·K) Results Heat losses (W/m²) 535 432 503 361 489 % decrease in — 19 633 9 heat losses compared to comparative example *comparative example

As it now clearly appears, the arrangement of the insulating material incavities limits the gas flows within the insulating layer, therebyconsiderably limiting the heat losses. As shown by the results given intable 1, a regenerator according to the invention can be up to 33% moreefficient than the regenerator in comparative example 1.

The invention further provides great flexibility in the design of theinsulating layer. In particular, the choice of the insulating materialis wider, in terms of its type, but also its form (powder, mixture offibers, etc.). The quality of the insulation may also be easilyadjusted, not only by the choice of the insulating material, but also bythe number and shape of the cavities and their filling ratio.

Furthermore, the arrangement of the insulating material in cavitiesallows it to be kept in place without any additional means for thispurpose. The fabrication of the insulating layer is thereby faster andcheaper.

The arrangement of the insulating material in cavities also reduces itscollapse (for powders, foams or fibrous mixtures in particular). Theeffectiveness of the insulating layer is thereby enhanced.

Finally, the arrangement of the insulating material in the cavitiesallows their protection from the environment prevailing in theregenerator, thereby increasing the service life of the insulatinglayer.

Obviously, the present invention is not limited to the embodimentsdescribed and shown, provided as examples. In particular, combinationsof the various embodiments described or shown also fall within the scopeof the invention.

Nor is the invention limited by the shape or dimensions of theregenerator.

Finally, the energy storage media may be in contact with a neutral orbasic environment.

1. A regenerator comprising a bed (11) of energy storage media (12)placed in a chamber (14), the chamber comprising a shell (20) and aninsulating layer (24) placed between said shell and said energy storagemedia or outside said shell, the insulating layer comprising a structuredefining a plurality of cavities (62 a, 62 b; 62′), each cavity having avolume greater than 5 cm³, at least a portion of said cavities beingfilled, at least partly, with an insulating material, the minimumthickness of the structural material separating the cavities and theinternal volume of the chamber wherein the energy storage media areplaced being higher than 2 mm.
 2. The regenerator as claimed in claim 1,in which the structure is made of a structural material having thefollowing chemical analysis, in weight percent based on the oxides andfor a total of 100%: 25%<Fe₂O₃<90%, and 5%<Al₂O₃<30%, and CaO<20%, andTiO₂<25%, and 3%<SiO₂<50%, and Na₂O<10%, and other oxides<20%.
 3. Theregenerator as claimed in claim 1, in which the structure is made of astructural material having the following chemical analysis, in weightpercent based on the oxides and for a total of 100%: 25%<Fe₂O₃<70%, and5%<Al₂O₃<30%, and CaO<20%, and TiO₂<25%, and 3%<SiO₂<50%, and Na₂O<10%,and other oxides<20%.
 4. (canceled)
 5. The regenerator as claimed inclaim 1, in which the structure is made of a structural material ofwhich more than 50% of the mass consists of one or more of the followingcompounds: iron oxides, alumina, magnesia, zirconia, silica, titaniumdioxide, and calcium oxide.
 6. The regenerator as claimed in claim 1, inwhich the structure is made of a structural material having: a chemicalcomposition identical to that of the material constituting the energystorage media and/or identical to that of the insulating material,and/or an open porosity lower than 20%, and/or a compressive strengthhigher than 10 MPa, and/or a pyroscopic resistance higher than 700° C.7. The regenerator as claimed in claim 1, in which the structureconsists of a bonding of structural blocks.
 8. (canceled)
 9. Theregenerator as claimed in claim 1, in which the minimum thickness of theinsulating layer is higher than 150 mm, and/or the thermal resistance ofthe insulating layer is higher than 1 m²·K/W.
 10. (canceled) 11.(canceled)
 12. (canceled)
 13. The regenerator as claimed in claim 1, inwhich the insulating material has a chemical composition such thatFe₂O₃+Al₂O₃+SiO₂+ZrO₂+B₂O₃+Na₂O+CaO+MgO+K₂O>60%, and/or the compound ofthe insulating material having the highest weight content is selectedfrom the group consisting of corundum, spinel MgAl₂O₄, calcined clays,mullite hibonite aluminum titanate bauxite and combinations thereof. 14.(canceled)
 15. (canceled)
 16. The regenerator as claimed in claim 1, inwhich the insulating material has the physical structure of a foam or ofa mixture of fibers.
 17. The regenerator as claimed claim 1, in whichmore than 50% by number of the cavities containing insulating materialare through cavities, and/or the cavities account for more than 50% ofthe volume defined by the structure and more than 50% by number of thecavities are filled at least partially with insulating material, and/orthe ratio of the volume of the insulating material of a cavity to thevolume of said cavity is higher than 50%.
 18. (canceled)
 19. (canceled)20. (canceled)
 21. (canceled)
 22. (canceled)
 23. The regenerator asclaimed in claim 1, in which the structural material and the insulatingmaterial are chemically substantially identical.
 24. (canceled)
 25. Theregenerator as claimed in claim 1, comprising at least first and secondcavities filled with first and second insulating materials,respectively, the first and second cavities having different shapesand/or volumes and/or bulk densities and/or orientations and/or fillingratios with the first and second insulating materials and/or the firstand second insulating materials having different chemical compositionsand/or physical structures and/or densities.
 26. The regenerator asclaimed in claim 1, in which the cavities are arranged so that anyimaginary straight line crossing the insulating layer in the directionof the thickness of said insulating layer necessarily passes through atleast one cavity.
 27. The regenerator as claimed in claim 1, in whichthe weight of the bed (12) is higher than 700 tonnes.
 28. A thermalinstallation comprising: a unit producing heat energy (4), and aregenerator (10) as claimed in claim 1, and a circulating device (7)which, during a charge phase, circulates a charge heat transfer fluidfrom the unit producing heat energy to the regenerator, and then throughsaid regenerator.
 29. The thermal installation as claim 28, in whichheat transfer fluid from said unit producing heat energy (4) condensesin said regenerator (10) in the form of an acidic liquid.
 30. Thethermal installation as claimed in claim 28, in which the temperature ofthe heat transfer fluid from said unit producing heat energy (4) andentering the regenerator is lower than 1000° C. and higher than 350° C.31. (canceled)
 32. The thermal installation as claimed in claim 28, inwhich the unit producing heat energy comprises a compressor.
 33. Thethermal installation as claimed in claim 28, comprising a heat energyconsumption unit (6), the circulating device (7) circulating, during adischarge phase, a discharge heat transfer fluid through saidregenerator, and then from said regenerator to the heat energyconsumption unit.
 34. (canceled)